1. Field of the Invention
The invention relates generally to the field of medical imaging and, more specifically, to transmission of medical imagery via a relatively narrow bandwidth client-server computer network such as the World Wide Web.
2. Description of the Related Art
The most common medical imaging techniques produce three-dimensional (3-D) data sets. Medical imaging techniques, such as computed tomography (CT), magnetic resonance (MR), positron emission tomography (PET), and single-photon emission computed tomography (SPECT), generate multiple slices in a single examination. Each such slice represents a different cross-section of the body part that is imaged. A simple transfer to the client computer of the result of the examination stored in the server's storage is obviously time consuming in a narrow bandwidth environment. This problem can be overcome by storing images in some compressed formats.
Data compression techniques can be roughly divided into two classes: lossy and lossless. Lossless compression techniques allow exact reconstruction of the original image, while lossy compression techniques achieve higher compression ratios, because they allow some acceptable degradation.
Although lossy compression is acceptable in many cases, lossless transmission is required in medical applications because lossy compression of images can lead to errors in diagnosis by introducing artifacts. Furthermore, there exist several legal and regulatory issues that favor lossless compression in medical applications. Although precise diagnosis require lossless representation of the study, lossy compression can be extremely useful for medical applications in which quick image browsing is desired. Therefore, the combination of lossy and lossless representations in a single workflow is desirable, with progressive lossy streaming of 3-D data terminating at lossless quality.
Because 3-D image data can be represented as a set of two-dimensional (2-D) images, it is possible to code these 2-D images independently. There exist several 2-D lossless compression algorithms, such as the LOw COmplexity LOssless COmpression of Images (LOCO-I) on which a lossless image compression standard called JPEG-LS is base, the Context-based Adaptive Lossless Image Codec (CALIC) algorithm and Compression with Reversible Embedded Wavelets (CREW). However, such 2-D methods do not utilize the inter-slice dependencies that exist among pixel values in the third dimension. A better approach considers the whole set of slices as a single 3-D data set taking advantage of correlation in all three dimensions.
Several methods that utilize dependencies in all three dimensions have been proposed for compression of 3-D data, both lossy and lossless, such as the Improved 3-D EZW (3D-IEZW); Modified EZW algorithm, used for compression of volumetric medical images; Context-based coding improvement of the EZW algorithm (3-D CB-EZW); a 3-D extension of Set Partitioning in Hierarchical Trees and Scalable Compressed Video coding algorithms. However, there is a common disadvantage of all the existing methods: they all need to store a compressed version of the original data, because the compression is very time consuming. These methods additionally lead to a tremendous growth of system memory usage. Wavelet compression is well known in the art. Conventional compression systems preferred wavelet bases of best coding performance.
A system and method for transmitting a digital image over a communication network is disclosed in U.S. patent application Ser. No. 6,314,452, “System and Method for Transmitting a Digital Image Over a Communication Network”, incorporated herein in its entirety by this reference That system and method does not address problems involved with lossless compression, and it does not specifically address 3-D images.
A system and method for a lossless wavelet transform in 2-D, having only the X and Y directions, is disclosed in U.S. patent application Ser. No. 60/198,017 “Lossless Progressive Streaming of Images Over the Internet” incorporated herein in its entirety by this reference. That system and method does not address 3-D images.